The invention relates to an article comprising carbon fibres which are bonded by carbon and to a method of producing an article comprising carbon fibres bonded by carbon.
It is known to use carbon fibres for reinforcing a matrix. One material from the which the matrix has been formed is carbon. In one common method of producing carbon fibre reinforced carbon, carbon fibres which have been coated with an organic resin are laid in a mould and the mixture of the fibres and resin is then compressed and heated to cause the organic resin to bind the fibres into a coherent body. This body is then further heated to carbonize the organic resin and thereby convert the deposit on the carbon fibres to carbon which binds the fibres together. Compression of the mixture of resin and fibres in the mould eliminates the presence of voids in the moulded mass and thereby contributes to the strength of the finished article. Strength is one of the main attributes of carbon fibre reinforced carbon.
Carbonization of the resin imparts a porous character to the article, volatile products of the carbonisation of the resin escaping through the pores and through any shrinkage cracks which are formed. The pores which result from carbonisation of the resin typically have cross-sectional dimensions of about three to five micron. An article having pores which generally have cross-sectional dimensions of less than ten micron is described herein as microporous.
Shrinkage cracks are likely to occur in any resin-rich region, that is a region substantially free of carbon fibre reinforcement. The cracks may have a width up to about 400 micron, depending upon the proportion of resin in the material occupying the region concerned.
It is known to increase the density of and improve the bonding of the fibres in microporous carbon fibre reinforced carbon by depositing further carbon in the pores and in any cracks. Carbon may be deposited in the pores (and cracks) by impregnating the article with a further quantity of organic resin and subsequently carbonising the resin or, alternatively, by depositing carbon in the pores (and cracks) from carbonaceous substances in the gaseous state. The latter technique is known as carbon vapour deposition. By one or other or a combination of these techniques, the pores (and cracks) are substantially filled so that the finished article does not have significant porosity.